The prior art discloses a large number of combustible non-tobacco materials which have been proposed as substitutes for tobacco in the preparation of smoking products. Most of these materials do not have colors that are typical of tobacco. Consequently, it is usually desirable to add coloring agents to such materials to improve acceptance by smokers who are accustomed to tobacco-like colors associated with smoking products they consume.
Various coloring agents and techniques have been disclosed in the art for imparting tobacco-like colors to tobacco substituents. For example, U.S. Pat. No. 3,638,660 discloses a tobacco substitute having appropriate dyes incorporated therein. U.S. Pat. No. 3,931,824 describes a cellulose-based tobacco substitute colored with agents such as carbon, iron oxide, food dyes, tobacco extracts, organic colorants and inorganic pigments. These agents are not entirely satisfactory because they may give rise to objectionable flavors upon smoking or they may be impractical due to economic considerations. Another technique for coloring tobacco substitutes is described in British Pat. No. 1,553,326 wherein tobacco dust comprising particles of 75 microns or less in diameter is applied to the surface of previously shredded tobacco substitute material to impart a tobacco-like color thereto. While that technique is effecitve, it also tends to defeat the purpose of adopting tobacco substitutes, namely, the elimination of tobacco from smoking products.
The prior art also discloses a number of agents which have been incorporated into smoking products for the purpose of altering the composition of smoke generated during the smoking process. Among the agents disclosed in vermiculite, a clay mineral comprising a hydrated form of iron magnesium aluminum silicate. The water of hydration in vermiculite is rapidly released upon heating at elevated temperatures thereby causing the vermiculite to expand. The expanded form vermiculite is a suitable filtration material for tobacco smoke as described in U.S. Pat. No. No. 2,786,741.
Unexpanded vermiculite has also been disclosed in U.S. Pat. Nos. 2,955,060 and 2,996,065 as a useful additive in smoking tobacco products at levels of 1 to 35 percent by weight using particle sizes in the range of about 200 to 600 microns. Heat released by the burning tobacco causes the vermiculite to expand and the expanded vermiculite acts as a smoke filtration agent located adjacent to the site at which the smoke is generated.
Various clay minerals are disclosed in U.S. Pat. No. 3,005,732 as tobacco additives capable of reducing the quantity of "tars" in the smoke generated by the treated tobacco and providing other benefits. Vermiculite is one of the minerals taught as being a suitable additive. These additives are used in the form of finely divided particles generally less than about 10 microns in size and, preferably, between 0.5 and 2 microns in size. The quantity of additive mixed with the tobacco is equivalent to 1-20 percent by weight of the tobacco.
The preparation of smokable products based on tobacco or cellulose-containing vegetable material is disclosed in U.S. Pat. No. 4,296,762 wherein combustion-modifying substances are incorporated into the products. The combustion-modifying substances disclosed include vermiculite and they are preferably applied to the surface of a paper-like web of tobacco or cellulose-containing material by immersing the web in an aqueous dispersion of the substance. The average diameter of the particles of combustion-modifying substances applied to the web is less than 2 microns and the quantity incorporated into the smokable product is between 0.1 and 10% by weight based on the total weight of the product.